An acrylic rubber obtained by polymerizing an acrylic acid alkyl ester or polymerizing an acrylic acid alkyl ester and an acrylic acid alkoxyalkyl ester is known as a rubber having cold resistance according to an environment for use and having excellent oil resistance particularly at a high temperature. Therefore, demand for the acrylic rubber is increasing as a hose for automobiles, an oil seal for automobiles, an O-ring for automobiles, a conveyor belt incorporated in a device or a machine, or the like. In recent years, further improvement of performance of rubber parts has been demanded, for example, because thermal environmental conditions around an internal combustion engine have become severe due to high output of the internal combustion engine, countermeasures for exhaust gas, or the like, and an engine oil is used under a high temperature condition without being exchanged for a long time to promote deterioration thereof due to contact with heat, air, water, exhaust gas, or the like.
For example, Patent Literature 1 discloses an acrylic rubber obtained by copolymerizing an acrylic acid alkyl ester, a specific ratio of a methacrylic acid alkyl ester, and a specific ratio of a cross-linkable monomer. Further, Patent Literature 2 discloses an acrylic rubber including a methacrylic acid alkyl ester unit, an acrylic acid alkyl ester unit and/or an acrylic acid alkoxy ester unit, and a carboxy group-containing α,β-ethylenically unsaturated monomer unit in specific ratios.